Saturday, February 20, 2016

A Truss Mirror Grinding Stand

Years ago I built a mirror grinding stand from 2x4s and plywood designed to be so solid that it could be rigid when bolted together--no glue was necessary. It was very, very heavy, which was great for stability but a bother to keep around the basement when not in use.

The club has been talking about a mirror-making workshop, and although it doesn't seem like something that's going to take place any time soon I was motivated to build something better for my mirror work. After looking around the Internet for designs I settled on something like the Stellafane design. It's a simple sort of truss barrel.

What I didn't like about the Stellafane design was 24" diameter of the top--it's too big for my purposes--and the four-corner truss. I decided to try a three-corner truss instead. The four-corner truss is a standard for big Dobs and is used by Starmaster, Teeter's, Discovery, and Obsession. The thee-corner truss has proven itself on Orion and Meade Dobs, so perhaps it would work well for ATM work. It's a little lighter and less work to assemble, too.

Because I was using a three-corner truss it seemed logical to make the top and base hexagonal instead of the circles used by Stellafane. My hexagons are inscribed in a 20" diameter circle, which will be of adequate size to handle any mirror I can foresee working on up to 12" diameter.

Here's what it looks like after first assembly:

The stand is 37" from floor to top, just right for me.

What you can't see is that there are three rubber feet under the base to help it sit flat on the floor without rocking. At this point it's held together by wood screws. It seems rigid enough, but I won't know how really solid it is until it's in use. There may very well be some glue in its future.

Still to be done is the addition of adjustable cleats for standard mirror sizes: 6", 8", 10", and 12" should do it. The entire assembly will get sealed with polyurethane, with the top getting a nice sanding and a triple coat of poly to resist the water it's going to see.

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